混合器停留时间分布的研究进展

研究混合器的停留时间分布对进一步研究混合器内的流型、混合等具有重要的意义。首先介绍了用于描述停留时间分布(RTD)的统计特征参量，根据测试原理及示踪剂输入方式等对停留时间的实验方法进行分类介绍。着重回顾了化学反应工程方法中RTD模型的发展，对有关RTD流场模拟中的常用模型进行了对比分析，并对统计学方法在RTD中的应用加...     

Advance in research on residence time distribution in mixers

研究混合器的停留时间分布对进一步研究混合器内的流型、混合等具有重要的意义。首先介绍了用于描述停留时间分布（RTD）的统计特征参量,根据测试原理及示踪剂输入方式等对停留时间的实验方法进行分类介绍。着重回顾了化学反应工程方法中RTD模型的发展,对有关RTD流场模拟中的常用模型进行了对比分析,并对统计学方法在RTD中的应用加以描述。最后展望了对上述方法在停留时间分布中的进一步应用。     

卧式双轴自清洁反应器粘性体系停留时间分布

在粘性体系中以茜素红为示踪剂,采用紫外光测试技术研究了卧式双轴自清洁反应器中的停留时间分布(RTD),利用返混模型对实验条件下的RTD及返混系数进行了模拟计算,得到了返混系数与雷诺数的关联式。结果表明,反应器的RTD受物料流速、搅拌速率及物料粘度等因素的影响,体系粘度增加返混系数减小;在实验范围内,基于返混模型的计算结果与实验结果基本相符。     

全息干涉法对气液流动浓度边界层的实验观测

引言 早期的界面浓度分布观测多采用加入示踪剂的方法[1-4].但由于示踪剂的加入对传质会造成干扰,影响了测量的可靠性.     

基于Cryptophane的甲烷光纤传感器研究进展

甲烷是天然气主要成分,煤矿开采过程中也产生大量甲烷气体,在其开采及运输过程中易发生泄漏爆炸,对甲烷浓度的实时监测具有现实意义。本文就近年基于cryptophane的甲烷光纤传感器研究进行了简单综述,包括消逝波吸收光纤传感器、模式滤光光纤传感器、荧光猝灭型光纤传感器、长周期光纤光栅传感器以及光子晶体光纤传感器。     

四传感器光纤探针测量气泡速度矢量模型

光纤传感器作为纤维光学领域中的新技术,在两相流动局部参数测量中得到了越来越广泛的应用。在假设气泡对称面垂直于气泡运动方向的基础上,对四传感器探针测量局部瞬时气泡速度的数学原理进行了详细推导,给出了新的计算气泡速度矢量的方法和模型,并运用自制的四传感器光纤探针,对气液两相流动中的气泡运动速度和方向进行了测量。实验中通过探针方法测得气相流速相对于流量计测量值的平均偏差为9%,表明新的探针测量方法精度较高,能够用于两相流中气泡速度矢量测量。进一步的实验研究表明,不同流动条件下,局部空泡份额及界面面积浓度(IAC)沿通道径向呈“壁峰型”或“核峰型”的分布规律。     

脉冲筛板萃取柱中连续相的轴向混合

通过示踪剂实验方法对38mm脉冲筛板萃取柱中连续相的轴向混合进行了研究。分别采用亚甲基蓝溶液和氯化钾溶液为示踪剂。实验过程中,首先采用"扰动-响应"技术实测了示踪剂的停留时间分布(RTD)曲线,然后依照轴向扩散模型(ADM)应用最小二乘法拟合求出连续相的轴向混合系数Ec,并分析了连续相表观流速、分散相表观流速、脉冲强度对于Ec的影响。实验结果表明,示踪剂浓度、径向取样位置和轴向取样位置对轴向混合系数Ec值的影响可以忽略,轴向混合系数Ec随着脉冲强度和两相表观流速的增加而增大。最后在本实验参数范围内,拟合出了连续相的轴向混合系数随操作参数变化的经验关系式,与实验结果对比,相对偏差在±20%以内。     

三相流化床液相径向和轴向扩散的研究

本文对二维扩散模型的示踪剂瞬态点源注入进行了解析及模拟计算.用微型电极检测不同径向位置的示踪剂浓度,由计算机对输出信号自动采集、实时分析,同时对三相流化床液相径向和轴向扩散系数等模型参数进行估值.     

微通道内低黏聚合物流体的停留时间分布研究

以低分子量的聚丙二醇为流动介质、酸性橙的N,N-二甲基乙酰胺溶液为示踪剂,采用脉冲响应法测定了螺旋型微通道（MC）反应器内的停留时间分布（RTD）,验证了平行多釜串联（PTIS）模型与RTD实验数据的匹配性,系统考察了MC长度和Reynolds数（Re）对RTD的影响,并讨论了流体径向速度分布指数y和Peclet数（Pe）的变化规律。结果表明,RTD随MC长度的增加而变窄。当通过降低黏度来增大Re时,RTD随之变窄。当通过增大流速来增大Re时,若管径较大,则RTD随之变窄。但若管径较小且管长不长时,则RTD随Re的增加而变宽;如管长较长,则RTD随Re（或流速）的增加先变宽后变窄,即存在临界Reynolds数（Re_c）。RTD的这些变化规律表明,二次流动和径向分子扩散对细小管径的MC的RTD有显著的影响。     

墙地砖表面平整度自动连续检测技术

墙地砖表面平整度自动连续检测采用光纤传感器测量采集数据，利用微机进行数据处理，评定等级，并输出分选控制信号，实现自动分选，码垛。该技术的使用，有利于提高检测效率，减少漏检率和保证检测精度。     

An optical device to measure in‐line residence time distribution curves during extrusion

This paper proposes a setup for in‐line measurement of residence time distribution (RTD) curves during extrusion. The detection system is composed of a slit die with transparent borosilicate glass windows fixed at the extruder exit, an optical arrangement with an incandescent light microbulb with fixed luminescence, and a Light Dependent Resistor (LDR) photocell of CdS. As the tracer passes through the light path, the reduction in the transmitted light intensity is followed by changes in the voltage induced by the photocell to an electric circuit. The signal is collected by an external interface and sent to a computer. Software acquires the data, does all calculations, and presents all curves and calculated variables to the monitor. The validation of the system was done by checking for data reproducibility and linearity with tracer concentration. The response of the LDR sensor with respect to the concentration of the tracer was calibrated using a set of slight dark film, obtaining a logarithmic relationship. Thus the signal enhances any disturbance, if present, particularly in the tail‐region of the curves. Measurements were taken from a Werner‐Pfleiderer ZSK 30 twin‐screw extruder equipped with K‐Tron gravimetric feeders operating with various screw speeds, feeding rates and screw configurations. In this last case, the presence of kneading elements was taken into account.     

磷光颗粒示踪技术在循环流态化中的应用

<正> 1 引言 固体颗粒的停留时间分布(Residence Time Distribution简称RTD)在循环流态化研究中十分重要,它对于了解其两相流动特性、反应器的模拟计算和工程设计是必不可少的,对于流态化干燥过程及传热行为的研究也很重要。流化床中RTD的研究已有大量文献报道,发展了诸如染色颗粒、盐颗粒、磁性颗粒、放射性颗粒及热(冷)颗粒等众多的示踪方法,但是由于固体颗粒示踪本身存在着示踪剂的注入、在线检测、残留及示踪颗粒与床体物料一致性、示踪过程对床内流场的干扰等一系列技术上的困难,不但使实验操作繁琐,而且实验结果的可靠性、重复性均不理想,特别是在颗粒运动速度较快的循环流化床中,其颗粒示踪的难度更大。为了解决上述难题,本文参考了Jin Yong等和Yu Zhiqing及M.Kwauk在常规流化床中曾采用的磷光示踪方法,在循环流化床条件下进行了新的探索。     

FREEZE DRYING WORLD UPDATE IN DRYING TECHNOLOGY

Spectral Sciences, Inc. is developing a multipoint humidity monitor for drying application in the pulp and paper industry. The humidity is measured by monitoring near-infrared optical absorption in the process stream atmosphere. An array of sensor heads distributed throughout the plant is linked by fiber optic cables to a single source/readout device which can be located in a control room hundreds of meters away. The sensor heads and cables are modular. allowing for raid installation and reconfiguration of a distributed sensor system in process control applications. The method used for quantifying the optical absorption provides substantial stability, accuracy, and signal processing advantages over standard wavelength scanning or band pass techniques. The laser diode's output wavelength is actively locked to the center of a water absorption line, thereby providing a constant monitor of water vapor concentration which is insensitive to all other species in the process stream. Wavelength modulation and second harmonic detection techniques are used to quantify the water vapor concentration. A simultaneous temperature measurement then permits an output of the absolute humidity or humidity ratio for process monitoring or control     

MULTIPOINT FIBEROPTIC HUMIDITY MONITOR

Spectral Sciences, Inc. is developing a multipoint humidity monitor for drying application in the pulp and paper industry. The humidity is measured by monitoring near-infrared optical absorption in the process stream atmosphere. An array of sensor heads distributed throughout the plant is linked by fiber optic cables to a single source/readout device which can be located in a control room hundreds of meters away. The sensor heads and cables are modular. allowing for raid installation and reconfiguration of a distributed sensor system in process control applications. The method used for quantifying the optical absorption provides substantial stability, accuracy, and signal processing advantages over standard wavelength scanning or band pass techniques. The laser diode's output wavelength is actively locked to the center of a water absorption line, thereby providing a constant monitor of water vapor concentration which is insensitive to all other species in the process stream. Wavelength modulation and second harmonic detection techniques are used to quantify the water vapor concentration. A simultaneous temperature measurement then permits an output of the absolute humidity or humidity ratio for process monitoring or control     

电导探针法测量高固含体系循环液速和气含率

基于电导探针和示踪法,开发了一种利用电导探针同时测量环流反应器中高固含体系下循环液速和局部气含率的方法. 利用2个单针电导探头测量脉冲注入KCl饱和溶液后两路电导信号的先后响应,测得两路液体的停留时间分布曲线. 通过对单路信号进行幅值分析可以得到气含率,与压差法相比测量值误差小于5%;通过对过滤气泡信号后的液体的停留时间分布曲线进行相关处理可得到循环液速,测量值与超声多普勒(UDV)的测量结果一致. 实验研究了外环流反应器中操作条件对气含率和循环液速的影响. 结果表明,低表观气速下气含率沿径向分布较均匀,高于0.1 m/s后逐渐呈抛物线型分布,整体随表观气速增加而增大;循环液速随表观气速增加近似线性增大,随固含率增加而减小.     

One-line measurement of the residence time distribution in screw extruders

A fluorescence monitoring device was constructed to measure in real time the residence time distribution (RTD) function in screw extruders. Its centerpiece was an optical fiber probe capable of transmitting optical excitation energy to the processed flow stream and detecting the subsequent fluorescence emission. The source of fluorescence emission was an anthracene-bearing substance that was injected to the flow stream as a pulse (tracer) in very small amounts. This device was validated against an off-line ultraviolet spectrophotometer and self-checked as well. In addition to its great sensitivity to fluorescence emission and ease of implementation on an extrusion line, this device could be used to monitor in real time subtle variations of an extrusion operation. The influence of the nature of anthracene-bearing compounds on the measured distribution and the effects of processing parameters on the RTD function were also investigated.     

Application of ultrasound in the determination of fundamental extrusion performance: Residence time distribution measurement

By means of new probe design and rapid data acquisition, we have succeeded in in‐line ultrasonic monitoring of residence time distribution (RTD) at the melting, mixing, and pumping zones as well as at the die exit of a Werner & Pfleiderer 30‐mm twin‐screw extruder by mounting the ultrasonic probes on the extruder barrel over the screw elements and at the die. The experimental systems were LDPE, CaCO₃‐filled LDPE, and a Kraton/LDPE blend. The ultrasonic data at each of the extruder functional zones are presented. The ultrasonic results have been used to evaluate an opical RTD measurement method by using an optical sensor side by side with one ultrasonic probe at the mixing zone of the extruder. The comparison of the ultrasonic and optical results has shown that the presented ultrasonic technique could be a good complement to the optical technique in the monitoring and understanding of RTD during polymer extrusion processes.     

Particle residence time distributions in circulating fluidised beds

This paper gives experimental measurements of the particle residence time distribution (RTD) made in the riser of a square cross section, cold model, circulating fluidised bed, using the fast response particle RTD technique developed by Harris et al. (Chem. Eng. J. 89 (2002a) 127). This technique depends upon all particles having phosphorescent properties. A small proportion of the particles become tracers when activated by a flash of light at the riser entry; the concentration of these phosphorescent particles can subsequently be detected by a photomultiplier. The influence of the solids circulation rate and superficial gas velocity on the RTD were investigated. The results presented are novel because (i) the experiments were performed in a system with closed boundaries and hence give the true residence time distribution in the riser and (ii) the measurement of the tracer concentration is exceedingly fast. The majority of previous studies have measured the RTD in risers with open boundaries, giving an erroneous measure of the RTD.Analysis of the results suggests that using pressure measurements in a riser to infer the solids inventory leads to erroneous estimates of the mean residence time. In particular, the results cast doubt on the assumption that friction and acceleration effects can be neglected when inferring the axial solids concentration profile from riser pressure measurements.An assessment of particle RTD models is also given. A stochastic particle RTD model was coupled to a riser hydrodynamic model incorporating the four main hydrodynamic regions observed in a fast-fluidised bed riser namely (i) the entrance region, (ii) a transition region, (iii) a core-annulus region and (iv) an exit region. This model successfully predicts the experimental residence time distributions.     

Characterization of the Residence Time Distribution in Spray Dryers

In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves.